KR20010081040A - Automatic repeat request protocol - Google Patents

Abstract

During communication between the first communication node and the second communication node, the first node receives a data unit sequence transmitted from the second node. The first incumbent node determines that the one or more transmitted data units were not received at all or were received incorrectly (ie, incorrect). Next, the first node sends one or more data unit retransmission requests that were not received or were incorrectly received to the second node. If a resend request is sent, the resend timer is activated. The retransmission timer indicates a delay time period required for the retransmission request to reach the second node, the second node to retransmit the requested data unit, and the retransmitted data unit to reach the first node. If the timer indicates that a delay time period has occurred / ended, the counter is activated. Based on the value of the counter, a determination is made as to whether all data units requested for retransmission have been correctly received. If the determination indicates that the requested one or more data units have been retransmitted and received correctly, no further action is performed. On the other hand, if one or more data units requested for retransmission are not received or are received incorrectly, the above described process is repeated.

Description

Automatic Resend Request Protocol {AUTOMATIC REPEAT REQUEST PROTOCOL}

Data packet communication is commonly a "best effort" packet delivery system. The best forwarding is to try to forward the packet carefully, that is, it does not discard the packet capriciously. In fact, data packet services are generally considered unreliable because delivery is not guaranteed secure, i.e., packets may be missed, duplicated, delayed, or misdirected.

However, many data communication applications require higher reliability or at least benefit from higher reliability. One way to increase transmission reliability is for two communication units to exchange response messages to know if a given message was successfully delivered and at what time. Increasing reliability by using positive and / or negative responses using retransmissions is generally referred to as an automatic repeat request (ARQ). More specifically, the transmitter sends a data unit to the receiver. If the data unit is received correctly, the receiver responds by sending an acknowledgment back to the transmitter. A negative response is sent if the data unit is not received correctly, i.e. if the data unit is received with an error (or at least too many errors to be efficiently corrected) and not with the data unit alone. In the negative acknowledgment situation, the receiver sends a data unit retransmission request to the transmitter that was not correctly received.

Next, the important point is when the retransmission decision of the data unit is made. One approach is to determine when to retransmit a data unit (eg, protocol data unit) using an ARQ timer. In particular, the timer can be started when the data unit is transmitted. If the timer expires before receiving an acknowledgment, the data unit is automatically resent.

The disadvantage of using the ARQ timer is that it is very difficult to set the ARQ timer to an optimal time-out value. If the time-out value is set too small, the ARQ timer tends to time out too early, ie before it can reasonably be predicted that a response is received. That is, when any additional time is prepared, a response is received, thereby preventing unnecessary retransmission requests and retransmission of data units. Thus, too small time-out values result in undesirable retransmission requests and retransmissions. Both of these waste communication resources which can be a problem in communication systems such as wireless communication systems where bandwidth is very limited. On the other hand, if the time-out value is set too large, a large and unnecessary delay occurs in retransmission request. This delay results in lower effective throughput of the communication system.

The problem of selecting an appropriate time-out value is further complicated for systems where the data transfer rate of the physical communication channel can vary. In systems such as third generation cellular telephone systems that provide a wide variety of services, the data transfer rate can vary very quickly, e.g. every radio frame (which can be on the order of 10 miliseconds). The optimal time-out value for one data rate may naturally be too long or too short for another data rate. Therefore, it is very difficult to obtain the optimal timeout by assigning the correct values in a changing environment.

The present invention relates to reliable data communication. In certain instances, the present invention relates to an automatic repeat request (ARQ) type of mechanism used to increase the reliability of communication. In the above example, the present invention can be used to improve the efficiency of such ARQ-based communication.

1 is a communication system in which the present invention may be employed.

2 is a flow diagram illustrating the implementation of the invention in one embodiment.

3 is a functional block diagram illustrating, as an example, a WCDMA wireless communication system in which the present invention may be advantageously employed.

4 illustrates a number of lower level communication protocol layers that may be used in the system shown in FIG.

FIG. 5 is a functional block diagram illustrating another implementation of the present invention in the system shown in FIG. 3. FIG.

6 is a diagram showing a predetermined example of the present invention.

7 is a diagram showing another predetermined example of the present invention.

8 is a diagram showing another predetermined example of the present invention.

It is an object of the present invention to provide effective and reliable data communication.

It is an object of the present invention to provide effective and reliable data communication in various situations.

Another object of the invention is to provide a mechanism for effectively determining the time at which one or more data units are received.

It is a further object of the present invention to provide automatic retransmission request (ARQ) processing that is optimally adapted to different communication situations, in particular to different channel transmission rates.

The present invention avoids the drawbacks of the simple timer method, thereby meeting the above-described object by allowing a communication unit to effectively and accurately determine when one or more data units are received in various situations. In particular, the present invention compensates for transmission delays and varying transmission rates. In the following, examples of the present invention are mainly disclosed in an ARQ-environment, but the present invention is more broadly applied to any communication situation where a receiver requires transmission of one or more data units and waits for the unit to be received.

During communication between the first communication node and the second communication node, the first node receives a data unit sequence transmitted from the second node. The first communication node determines that one or more transmitted data units were not received at all or were received incorrectly (ie, corrupted). Next, the first node sends a request to the second node for one or more data unit retransmissions that were not received or were incorrectly received. When a resend request is sent, the resend timer starts. The retransmission timer describes the time required for the retransmission request to reach the second node, the time required for the second node to process the request, and the time required for the first retransmitted data unit to reach the first node.

If the timer indicates that the delay time period has ended, the counter is started. According to the value of the counter, a determination is made as to whether all data units requested for retransmission have been correctly received. If a determination is made that the requested one or more data units have been retransmitted and received correctly, no further action is taken. On the other hand, if the requested one or more data units are not received or are received incorrectly, the process described above is repeated.

This timer is preferably started at the same time as sending the retransmission request from the first node to the second node. The counter is also preferably started at or before starting the timer. The count value is changed after each time interval while multiple data units are being transferred between the first and second nodes. One example of such a time interval is a communication frame. In an embodiment, the counter increments after each time interval by the number of data units received during that time interval. For example, if two data units are currently sent in each time interval, the counter is incremented by two. When the count value reaches the number of retransmission requested data units, this is a good time for the first communication node to determine whether the retransmission requested data units have been received correctly. At this point, the requested data unit is retransmitted by the second communication node and received by the first communication node.

As described above, the present invention can be advantageously used in any transmission request for the data unit. By indicating a round trip delay of a given data unit transmission request, the counter starts counting the expected data units at a suitable time to predict that the requested unit can be postmarked and received. The counter is adjusted to change the transmission rate on the communication channel by changing the count value only by the number of data units received at each time interval. Thus, a lower transmission rate provides more time effectively, while a higher transmission rate allows less time. As a result, there is an effective and optimal balance between delay (waiting too long to request a retransmission when the requested data unit is not received correctly) and unnecessary retransmission requests and retransmissions (before the data unit has a reasonable chance of being received). Will fit.

A preferred embodiment of the present invention is disclosed in a wideband code division multiple access (WCDMA) wireless communication system environment. In the situation illustrated above, the present invention is performed as an automatic retransmission request technique implemented in a radio link control (RLC) communication protocol layer. The ARQ technique is implemented in the RLC layer of both mobile stations and radio access networks using counters and timers. The counter stores a count value indicating the number of data units to be resent. The timer causes the counter to start counting after the time interval associated with the resend request. The present invention is particularly advantageous in such a situation because the data transmission rate in the wireless channel can vary greatly from frame to frame.

The above and other objects, features and advantages of the present invention will become apparent from the following description of the preferred embodiments as shown in the accompanying drawings, wherein the reference characters refer to the same parts throughout the several views. The drawings are by no means for comparison, but instead for emphasis in describing the principles of the invention.

DETAILED DESCRIPTION Hereinafter, for the purpose of explanation and not limitation, details of certain embodiments, data flows, signal implementations, protocols, techniques, etc. are set forth in order to provide an understanding of the present invention. However, it will be apparent to one skilled in the art that the present invention may be practiced in other embodiments that depart from these specific details. For example, although embodiments of the present invention have been disclosed with respect to certain protocol layers, ie, link layers, those skilled in the art will recognize that the present invention may be implemented in any suitable communication protocol or protocol layer. In other instances, detailed descriptions of well-known methods, interfaces, devices and signal techniques have been omitted so as not to obscure the description of the invention with unnecessary details.

1 shows a communication system 10 comprising a first communication unit 12 and a second communication unit 14. The data unit (which may include substantial message information, control information, or both) is communicated from the first communication unit 12 to the second communication unit 14 by a suitable communication medium. An example of a non-limiting data unit is a protocol data unit (PDU); However, larger, smaller, or differently shaped data units may also be used. If the second communication unit 14 detects that one or more data units have not been received or were received incorrectly, the second communication unit sends a request for retransmission of the detected data unit to the first communication unit 12. .

Thereafter, if the second communication unit 14 does not receive the requested data unit by a predetermined time point, it transmits another request for retransmission of the same data unit as above. The predetermined time point is determined using a two step process. First, when a retransmission request is sent, the second communication unit 14 expects that the first communication unit 12 receives and processes the retransmission request and the second communication unit 14 receives the first retransmitted data unit. Wait for a defined time period corresponding to the round trip delay. Then, after the prescribed time period has elapsed, the second communication unit 14 then counts up (or counts down from) the number of PDUs to be received. When the counter reaches the number, if all of the requested data units are not received, another request for retransmission of the data units is sent.

2 shows an Automatic Retransmission Request (ARQ) routine (block 20) that embodies a non-limiting implementation of the invention. A receiving communication unit, such as unit 14 of FIG. 1, receives a data unit transmitted by a transmitting communication unit, such as unit 12 of FIG. 1 (block 22). The communication unit 14 determines that one or more data units were not received or were received incorrectly (block 24). Next, communication unit 14 requests retransmission for the one or more data units (block 26). Simultaneously with or at the time the retransmission request is sent, the second communication unit also operates a retransmission timer (block 28). The retransmission timer generates an output after a defined retransmission time period that indicates the transmission and delay for the transmission of the actual retransmission request. It also represents processing time and other conditions / parameters in both communication units.

The end of the retransmission time period corresponds to when the first data unit requested for retransmission is received. At this time, the communication unit 14 activates the data unit counter (block 30). Thereafter, the data unit count value in the counter is changed by increasing (or, optionally, decreasing from 0 to 0) to a count value corresponding to the number of data units received. The count value is changed for each transmission time interval, e.g. at the end of the transmission frame, by a number corresponding to the number of PDUs to be received during the transmission time interval based on the current transmission rate (block 32).

When the data unit count value reaches the number of retransmission requested data units, the communication unit 14 determines whether the requested data unit has been correctly received (block 34). If received correctly, the communication unit 14 continues to receive a new data unit from the communication unit 12. In addition, communication rest 14 may send an acknowledgment to communication unit 12 that the requested data unit was received correctly. On the other hand, if any of the requested data units are not received correctly until the data unit counter reaches an appropriate count value, the retransmission timer and counter are reset (block 36) and the process starting at block 26 is repeated. do.

One application of the present invention is now described with respect to the universal mobile telecommunications system (UMTS) 50 shown in FIG. Representative connection-oriented external core networks (illustrated as cloud 52) include, for example, a Public Switched Telephone Network (PSTN) and / or an Integrated Service Digital Network (ISDN). ) And the like. Representative connectionless-oriented external core networks (shown in cloud shape 54) are, for example, the Internet. Both core networks are connected to the corresponding service node 56. The PSTN / ISDN connected network 52 is connected to a connected service node, shown as a mobile switching center (MSC) node 58 that provides circuit-switched services. In the existing GSM model, mobile switching center 58 is connected to base station system (BSS) 62 by interface A, which is connected to wireless base station 63 by interface A '. ) Is connected. The Internet connectionless network 54 is connected to a General Packet Radio Service (GPRS) node 60 for the purpose of providing packet switched services.

Each of the core network service nodes 58 and 60 is connected to a UMTS Terrestrial Radio Access Network (UTRAN) 64 by the UTRAN interface I _u . UTRAN 64 includes one or more wireless network controllers 26. Each RNC 66 is connected to a plurality of base stations (BS) 68 and other RNCs in the UTRAN 64. Wireless communication between the base station 68 and the mobile radio station (MS) 70 is through a wireless interface. Radio access is based on Wideband-CDMA (WCDMA), where individual radio channels are assigned using CDMA spreading codes. WCDMA guarantees high quality by providing wide bandwidth for multimedia services and other high-speed needs as well as powerful features such as diversity handoffs and RAKE receivers.

The air interface shown in FIG. 3 is divided into several protocol layers with multiple lower level layers shown in FIG. In particular, mobile station 70 orchestrate communication with similar protocol layers in UTRAN 64 using the protocol layers. Both protocol stacks include a physical layer, a data link layer, and a network layer. The data link layer is divided into two sublayers: a radio link control (RLC) layer and a medium access control (MAC) layer. In the above example, the network layer is separated into a control plane protocol (RRC) and a user plane protocol (IP).

The physical layer uses broadband CDMA to provide information transfer services over the air interface, and includes the following features: forward error correction encoding and decoding, macrodiversity distribution / combination, soft handover execution, error detection, and multiplexing of transport channels. Demultiplexing, transmission channel mapping over physical channels, modulation and spreading / demodulation and despreading of physical channels, frequency and time synchronization, power control, RF processing, and other functions.

The intermediate access control (MAC) layer provides unauthorized transfer of service data units (SDUs) between peer MAC entities. The MAC function selects the appropriate transmission format for each transport channel according to the data transmission rate, prioritizes between one user's data flows and between different user's data flows, scheduling control messages, multiplexing and demultiplexing of upper layer PDUs, etc. Includes features. RLC establishes, releases, and maintains RLC connections; splits upper layer PDUs of varying length into smaller RLC PDUs; It performs various functions including error correction using (ARQ), sequentially transmitting higher layer PDUs, double detection, flow control, and the like.

The control surface portion of the network layer of the UTRAN consists of Radio Resource Control Protocol (RRC). The RRC protocol processes control signals over the air interface, such as radio access bearer control signals, measurement reports and handover signals. The user-side portion of the network layer includes the typical functions performed by Layer 3 protocols, such as the well known Internet Protocol (IP).

FIG. 5 is a functional block diagram illustrating an example implementation of the invention in the RLC layer of a UMTS entity, such as mobile station 70, or in the RLC layer of RNC 66 shown in FIG. In the RLC layer implementation, overall RLC layer operation and various predetermined RLC layer functions can be monitored and generally controlled by the RLC controller 80. Although certain functional blocks are shown in FIG. 5, the functions may be performed using any suitable hardware and / or software. For example, a counter or timer can be implemented in hardware or software.

At the transmitting side of the communication entity at the RLC layer, higher layer packets are received at segmentation, concatenation, and additional RLC header block 82. Upper layer packets are divided and / or concatenated into PDUs of constant length. The PDU length is determined when a given radio access network service is established for communication involving a given mobile station. Once the RLC header is added to each PDU, they are stored in both the retransmission buffer 86 and the transmit buffer 90 via the selector. Next, the PDUs stored in the transmit buffer 90 are transmitted by the air interface according to the flow control signal from the RLC controller 80 to the lower MAC layer for transmission to the receiver via the physical layer. When a request for one or more PDU retransmissions is received (eg, ACK, NACK, or SACK), the RLC controller 80 controls the selector 88 to select a PDU stored in the retransmission buffer 86 to transmit buffer 90. Send via

At the receiving end of the communication entity at the RLC layer, the PDU is received from a logical channel from the MAC sublayer. The received PDUs are placed in receive buffer 98 and then processed by detection and analysis block 96. Block 96 sends the correctly received PDU to block 84. In block 84, the RLC header is removed from the PDU, which is then reassembled into higher layer packets that are forwarded to the higher protocol layer.

If the detection and analysis block 96 detects that a PDU is missing or incorrectly received, a retransmission request signal is generated, for example in the form of a negative acknowledgment (NACK) or an optional acknowledgment (SACK). The retransmission request is sent to the RLC controller 80. The retransmission request receives the priority in the transmit buffer 90 with respect to the other PDUs waiting to transmit using the appropriate control signals from the RLC controller 80 to the retransmit buffer 86, the selector 88 and the transmit buffer 90. do.

Simultaneously with or at the time a retransmission request is generated, detection and analysis block 96 also operates an estimated PDU counter (EPC) timer 94. The EPC timer 94 is set to a retransmission time corresponding to the round trip propagation delay of the retransmission request and initial response, processing time at the transmitter and receiver, and time to compensate for the frame structure. If the EPC timer 94 indicates that the retransmission time is up, then the estimated PDU counter (EPC) 92 is enabled or activated. The EPC timer 94 may also be implemented as a counter that counts the number of radio frames that are expected to pass before the first retransmission requested PDU is actually received.

The EPC 92 may be set to increase up to the number of PDUs requested to be transmitted, and may optionally be selected to decrease up to the number of PDUs requested to be transmitted. In the above example, the EPC 92 is incremented every physical link (L1) time period, which is typically one radio frame, but the L1 period may be more than one radio frame. Within the L1 time period, an integer number of PDUs are transmitted. The integer depends on the size of the PDU and the speed at which the PDU is sent.

In UMTS 50, it is possible to change the transmission rate after every L1 time period. Thus, the number of PDUs may vary. The transmission rate information bits are transmitted simultaneously with the data DPU from the MAC layer and used by the RLC controller 80 to determine the transmission rate for the current L1 time period. Next, the RLC controller estimates the number of PDUs transmitted during the L1 time period. EPC 92 is incremented every L1 time period by an estimated number of PDUs transmitted during the current L1 time period (provided by RLC controller 80 based on the most recent reception rate information received from the MAC layer). (Or decrease).

When the EPC 92 reaches the number of outstanding PDUs required for retransmission, the detection and analysis block 96 detects whether the requested PDUs were actually correctly received upon retransmission. If received correctly, the reception and processing of the new PDU is followed. However, if one or more PDUs required for retransmission were not correctly received when determined by detection and analysis block 96, EPC 92 and EPC timer 94 are reset. In addition, a new retransmission request is sent requesting (re) retransmission of the outstanding PDU. The EPC timer 94 is restarted, and the above described process is repeated.

Reference is now made to FIG. 6, which shows some examples. The transmitter transmits four PDUs with sequence numbers (0, 1, 2 and 3) at high transmission rates (ie four PDUs per L1 frame). PDUs 1 and 2 are missing or incorrectly received. Thus, the receiver sends an optional acknowledgment (SACK) back to the transmitter requesting to retransmit the PDUs 1 and 2. At the same time, the EPC is set to zero and the EPC timer is running. Each arrow from the transmitter to the receiver represents an L1 time period. In the next L1 time period, the transmitter further sends four data PDUs corresponding to the sequence numbers 4, 5, 6 and 7. Thereafter, the transmission rate is reduced from four PDUs per L1 time period to one PDU per L1 time period.

Next, the transmitter receives a SACK message from the receiver requesting retransmission for the PDUs 1 and 2. Since the retransmission request has a higher priority, the transmitter retransmits the PDU 1 for the next L1 time period. Currently, only one PDU is transmitted during one L1 time period at a lower transmission rate, so the transmitter transmits only one PDU 8 for the next L1 time period. After receiving the PDU 8, the EPC timer that enables the EPC counter ends. If the next L1 time period occurs corresponding to the retransmission of the PDU 1, the EPC is increased by one.

Recall that rate information is provided concurrently with the data and, in one implementation, may be included in the transmission format information provided by the MAC layer. The transmission format information indicates how many RLC PDUs are received for each radio frame. During the next L1 time period, the retransmitted PDU 2 is received and the EPC increases to two. Here, the receiver performs a check to determine whether all PDUs requested for retransmission have been correctly received. Since both retransmitted PDUs (1 and 2) have been received correctly, both the transmitter and receiver continue as before retransmission.

However, situations may arise where one or more retransmitted PDUs are missing or incorrectly received. 7 shows an example of such a situation. FIG. 7 is similar to that shown in FIG. 6 except that the first retransmitted PDU 1 is not received correctly by the receiver. However, at the end of the L1 time period at which the PDU 1 should be received, the EPC increases by one. At the end of the L1 time period, the PDU number 2 is correctly received and the EPC is increased to two. At this time, a determination is made that the PDU was received incorrectly even though the PDU 1 should be received by this point. Thus, the receiver sends another optional response back to the transmitter requesting retransmission for the PDU 1.

Upon this second retransmission request, the EPC counter is initialized to zero and the EPC timer is activated again. The PDU 9 is received at the end of the next L1 time period. The transmission rate is increased to two PDUs per L1 time period, so that both PDUs 10 and 11 are transmitted during the next L1 time period. The transmitter receives the second retransmission request and transmits the requested PDU 1 with the next predetermined PDU 12 during the next L1 time period. However, just before this, the EPC timer, which enables the EPC counter, ends. If the next L1 time period is issued corresponding to the reception of the PDUs 1 and 2, the EPC increases to one. At this time, the detection and analysis block 96 determines that the requested PDU 1 has been received correctly and in fact. Thereafter, both the transmitter and the receiver continue as before retransmission.

There may also be situations where the EPC timer is set to a value that is too large or too small. For example, FIG. 8 shows an example of a situation in which the EPC timer is set to a time-out period that is too long. As shown, PDUs 1 and 2 are not properly received. The EPC timer starts immediately after the PDU 3 is received, which is when the receiver detects that the PDUs 1 and 2 have not been received correctly. The receiver sends a SACK message listing the PDUs 1 and 2 to the transmitter. Since the EPC timer is set to a time-out value that is too large, the retransmitted PDU 1 is received before the EPC timer expires. Thus, when the required number of PDUs is received (1 in the above case), the EPC starts anyway. Next, when the retransmitted PDU 2 is received, the EPC increases to two. At this time, the receiver determines that all required PDUs have been received correctly.

In contrast to a simple time-out approach that results in large transmission delays and unnecessary retransmission requests / retransmission results, the present invention adjusts to changing transmission conditions and provides an optimal time to determine if an expected data unit has been reached. By indicating a round trip delay of a given data unit transfer request, the counter begins counting the expected data units at a point in time to predict that all required units have been transmitted and received. In addition, the counter is adjusted for changing conditions such as too long or too short EPC timer values and changes in transmission speed on the communication channel. In the latter case, the count value is changed by the number of data units received during each time interval. Lower transmission speeds provide more time effectively, while higher transmission rates allow less time. Thus, the present invention balances delay and retransmission requirements and retransmissions in an effective and optimal state.

Although the present invention has been described in connection with certain embodiments, those skilled in the art will recognize that the present invention is not limited to any of the embodiments described herein. Various forms, embodiments, and adaptations other than those shown and described above, as well as numerous variations, variations, and equivalent devices, may be used to implement the present invention. Thus, while the invention has been described in connection with embodiments for the ARQ protocol, it should be noted that the above embodiments are non-limiting examples of the invention. The present invention is generally applicable to situations where a data unit is required to be transmitted and the requestor needs to determine when the data unit has been received. Accordingly, it is intended that this invention be limited only by the intent and scope of the appended claims.

Claims (41)

A first communication node capable of communicating with a second communication node, Sending a request to a second node requesting transmission of one or more data units, Starting a counter after a time period associated with the send request, and Based on the value output by the counter, determining whether the requested one or more data units have been received. The method of claim 1, Prior to the transmitting step, Receiving a data unit transmitted from the second communication node, and Determining whether one or more transmitted data units were not received or were received incorrectly, The transmitting step includes requesting retransmission for one or more data units that were not received or were received incorrectly, And the counter starts after a time period associated with the retransmission request. The method of claim 2, If the one or more requested data units are not received or are received incorrectly, repeating the transmitting, starting and determining step. The method of claim 1, Providing a counter controller to set the time period. The method of claim 4, wherein The counter controller is a timer, the method comprising: Starting a timer when the request is sent, and Setting the counter to an initial value at or before the timer expires. The method of claim 5, And when the timer reaches a time period, the counter counts to provide an estimate of the number of data units received from the second node. The method of claim 5, And if the requested PDU is received before the time period ends, a counter starts counting from the requested PDU. The method of claim 4, wherein The counter controller is another counter that counts time intervals to estimate a time period. The method of claim 1, Changing the count value after a time interval at which a plurality of data units can be transmitted has ended. The method of claim 9, And the count value increases after each time interval until the count value matches the number of data units received from the second node. The method of claim 10, If one or more data units are not received or are incorrectly received when the count value matches the number of data units to be received from the second node, then the method: Resetting the time period, Requesting to retransmit one or more data units that were not received or were received incorrectly, Resetting the counter, and Starting the counter after the set time period has ended. The method of claim 9, The time interval corresponding to a frame on a communication channel between the first communication node and the second communication node. The method of claim 12, And the time interval corresponds to a plurality of frames. The method of claim 12, The communication channel is a wireless channel, and the time interval is a wireless frame on the order of 10 milliseconds. The method of claim 9, An integer number of data units are transmitted during the time interval. The method of claim 9, The counting value is changed to the number of data units to be transmitted during the time interval at every time interval. The method of claim 1, Wherein said time period corresponds to a round trip delay associated with transmitting information to a first communication node and receiving information back from the first communication node. A communication monitoring method for monitoring communication between a transmitter and a receiver in a wireless communication system in which a protocol data unit (PDU) is delivered by a wireless communication channel between a transmitter and a receiver, and a data unit is transmitted for a predetermined channel time interval, (a) detecting that a PDU sent by the transmitter was not received correctly by the receiver, (b) sending from the receiver to the transmitter a message requesting to retransmit the PDU; (c) starting the time monitor with the transmission of the message, (d) starting the PDU counter after the time monitor indicates that the prescribed time interval has elapsed, (e) changing the value of the PDU counter after the end of the prescribed next radio time interval, and (f) determining, based on the value output by the estimated PDU counter, whether the requested PDU has been received correctly. The method of claim 18, After the prescribed next radio time interval, the value in the PDU counter is changed according to the number of PDUs to be delivered to the receiver during the prescribed next time interval. The method of claim 18, Repeating steps (b)-(f) if the PDU counter reaches a count value indicating that the requested PDU was received correctly by the receiver, and if the requested PDU was not received correctly at the receiver. Communication monitoring method characterized in that. The method of claim 18, In response to a change in transmission rate, different numbers of PDUs may be transmitted during one of the defined wireless time intervals. The method of claim 18, And wherein said message is an optional response message sent on a radio link control (RLC) communication protocol layer. The method of claim 18, And if the requested PDU is received before the end of the time period, the counter starts counting from the requested PDU. The method of claim 18, And the timer monitor is another counter that counts time intervals to estimate a prescribed time period. As a communication unit for a communication system, A receiver receiving a data unit by a communication channel from another communication unit, A transmitter for transmitting a request for transmitting a plurality of data units to a communication unit to another communication unit, A counter having a count value indicating the number of data units to be transmitted, and A time monitor that causes the counter to begin counting after the time interval associated with the send request has ended, The communication unit uses the count value to determine whether the number data units have been transmitted and received correctly. The method of claim 25, Wherein said data unit is delivered via a communication channel in a channel frame, and a counter is incremented after one channel frame has passed. According to claim 25, An integer number of data units are transmitted during one channel frame, and the integer number of data units for each channel frame may be different for each different channel frame. The method of claim 27, And the number of data units transmitted during the one channel frame varies depending on the size of the data unit and the transmission speed of the data unit. The method of claim 25, A time interval associated with the transmission request transmits a transmission request to another communication unit to estimate a time required for the communication unit to receive the transmitted data unit. The method of claim 25, The communication unit is a mobile station having a radio link control (RLC) protocol layer comprising a time monitor and a counter. The method of claim 25, Said communication unit being a radio network controller in a radio link control (RLC) protocol layer comprising a timer and a counter. The method of claim 25, Said communication system is a wireless communication system and said communication unit is a mobile station. The method of claim 25, The communication system is a wireless communication system and the communication unit is a wireless network node. The method of claim 25, And if the requested PDU is received before the end of the time period, the PDU counter starts counting from the requested PDU. The method of claim 25, The timer monitor is another counter for counting time intervals to estimate the time intervals. A first communication unit operating method, Receiving at the first communication unit a data unit transmitted by the second communication unit via a communication channel, Requesting the second communication unit to send one or more data units to the first communication unit, and Determining at the first communication unit when the requested one or more data units are received, including compensating for a delay corresponding to the transmission request and a current transmission rate on the communication channel. . The method of claim 36, The delay is compensated using a timer, and the current transmission rate is compensated using a counter. The method of claim 37, If the timer indicates that the prescribed time period corresponding to the delay has ended, the counter starts counting to determine when the requested one or more data units have been received by the first communication unit. How the unit works. The method of claim 38, And if the requested one or more data units are not received when the counter reaches a predetermined count value, sending a retransmission request to a second communication unit. The method of claim 39, And the predetermined count value corresponds to the number of data units received by the first communication unit. The method of claim 36, And the second communication unit is required to retransmit one or more data units to the first communication unit.